86 THE GLACIAL PHENOMENA OF THE COUNTRY 



been in part scooped out since the ice passed away. Others 

 possibly date from the time of the glacial lakes, as will be 

 shown later. Those which are intercalated with the clay have 

 naturally been formed during the Ice Age itself. 



The Pre-glacial Surface. — The general contour of the 

 country before the oncoming of the ice can be made out from 

 field observation by mapping the height of the rock exposed, 

 and this is supplemented where the drift is thick by informa- 

 tion derived from borings and sinkings. This method has 

 been admirably applied to the case of the " Wash " by Wood 

 and Boyd*, and more recently to the Northumberland and 

 Durham Coalfield by Woolacott.f 



Viewing the district under consideration broadly, v/e may 

 say that above the 400-foot contour the surface of the land, 

 and consequently the drainage system, was much the same in 

 pre-glacial times as it is now, with the difference that the 

 valleys were deeper and the country as a whole had more 

 character. Below that level, however, many of the old 

 features have been obliterated by the accumulation of drift, 

 and at times this has resulted in the setting-up of a new 

 drainage system. 



The main facts deducible about the old land-surface are 

 these : — Much of the country in the west of the area was then, 

 as now, of a gently undulating character, sloping gradually 

 eastwards from the watershed and supplying the head-waters 

 of a number of burns which flowed down the dip-slope of the 

 rocks. Only one of these burns attained to any size and cut 

 deeply into the land ; this was the pre-glacial " Blyth,"| the 

 modern representative of which, flowing in much the same 

 direction, is still the most important stream of the district. 



Coming now to the country below the 400-foot contour,§ 

 there were several long unbreached ridges which formed the 



* Trans. North of Eiig. Inst. Min. Eng\, vol. xiii., p. 69 (1863-4). 



t Op. cit. 



J lu futiu-e the inverted commas used with snch names will refer only to the 

 pre- rjlacial streams. 



§ That is present level. It should be remembered that the country as a whole 

 stood much higher in pre-glacial times than it does now. 



